This seal has caused far more debate among commentators than any other. There are dozens of plausible (and not a few implausible) suggestions for what this short period of silence means. It is possible this is simply a rhetorical pause, the calm before the storm.
Some see it connected to the Jewish practice of silent prayer, which is connected to incense burning found in the same context as the silence. In the context of chapter 8 this is possible, since the angels are lighting incense in the temple of God. David Aune offers several rabbinic texts implying a ritual silence was practiced during the burning of the incense (m. Tamid 5:1-6 does not explicitly say that the incense was offered in silence; 2:508). This suggestion has some merit, since silence is associated with worship of God in the Old Testament (Psalm 46:10) and even among the Greeks (Thucydides, for example).
Thuc 6.32.1 The ships being now manned, and everything put on board with which they meant to sail, the trumpet commanded silence, and the prayers customary before putting out to sea were offered, not in each ship by itself, but by all together to the voice of a herald; and bowls of wine were mixed through all the armament, and libations made by the soldiers and their officers in gold and silver goblets.
Greg Beale observes silence is associated with Gods judgment. The nations are silenced when they fall under God’s judgment (Revelation, 446). In Isaiah 47:5 Babylon is told to “sit in silence,” in Ezekiel 27:32, Tyre is silenced. Zephaniah 1:17 the day of the Lord is an occasion for silence because it is like a sacrifice to the Lord.
Isaiah 47:5 “Sit in silence, go into darkness, Daughter of the Babylonians; no more will you be called queen of kingdoms.
Ezekiel 27:32 As they wail and mourn over you, they will take up a lament concerning you: “Who was ever silenced like Tyre, surrounded by the sea?”
Zephaniah 1:7 Be silent before the Sovereign LORD, for the day of the LORD is near. The LORD has prepared a sacrifice; he has consecrated those he has invited.
Both silence in judgment and silence as worship appear in the pseudepigrapha. In 1 Enoch 18:2, Enoch sees the fifth heaven where encounters the innumerable armies called Grigori” (the watchers) who had turned aside from the Lord. The gigantic beings are perpetually silent and “there was no liturgy in the fifth heaven.” In 4 Ezra 7:30, after the messiah dies “the world shall be turned back to primeval silence for seven days.”
The Letter of Aristeas describes Temple worship as “well ordered silence” (92), “a general silence reigns, so that one might think that there was not a single man in the place although the number of ministers in attendance is more than seven hundred” (95). The Testament of Adam begins with a list of the twelve hours, concluding with “the twelfth hour is the waiting for incense, and silence is imposed on all the ranks of fire and wind until all the priests burn incense to his divinity” (1.12). Notice the connection between silence (Rev 8:1) and incense (Rev 8:2-5).
I think it is best to see the seventh seal, trumpet, and bowl as parallel. Just prior to God’s intervention to defeat his enemies (the seventh bowl), there will be worship in heaven. First, this is silence, but it is followed by loud worship. Revelation 12:15 says when the seventh trumpet sounds, there were “loud voices in heaven” because the kingdom of God has come.
Why “about a half an hour?” Once again, there are dozens of suggestions. It is a short and indefinite time, much like Daniel 4:16,19, Daniel was amazed and struck with silent awe for about an hour. Later in Revelation, several judgements all take place within an hour (18:10, 17, 19).